Pressurized baseboard-type electrical heater and method of charging same



Oct. 25, 1966 5. J. HEIMAN 3,281,574

PRESSURIZED BASEBOARD-TYPE ELECTRICAL HEATER AND METHOD OF CHARGING SAME Filed March 16, 1964 2 Sheets-Sheet 1 AIR SUPPLY INVENTOR- SIDNEY J. HEIMAN ATTORNEY Oct. 25, 1966 Filed March SOUND LEVEL S. PRESSURIZED BAS J. HE'IMAN EBOARD-TYPE ELECTRICAL HEATER AND METHOD OF CHARGING SAME TIME (MIN) FIG.4

2 Sheets-Sheet 2 INVENTOR SIDNEYJ. HEIMAN AT TO RN EY United States Patent 3 281,574 PRESSURIZED BASEfiOARD-TYPE ELECTRICAL HEATER AND METHOD OF CHARGING SAME Sidney J. Heiman, University City, Mo., assignor to International Oil Burner Company, St. Louis, Mo., a corporation of Missouri Filed Mar. 16, 1964, Ser. No. 352,259 5 Claims. (Cl. 219341) The present invention relates generally to an electrical powered baseboard heater and more particularly to both method and apparatus for suppressing noises commonly experienced in such electrical baseboard heaters.

Prior art heater units of the general type have either had open expansion tubes or expansion tubes in which air was sealed under atmospheric pressure. The use of such heating units has been accompanied by long periods of noise during start up and thermostatic cycling. The cause of these noises and vibrations of the metallic heater have not been fully understood; but factors which contribute thereto are discussed hereinafter.

I have discovered that the use of a sealed expansion tube in such heaters, when charged with a gas under pressure, substantially greater than atmospheric pressure, greatly decreases the time interval during which such noise is manifest and tends to suppress the magnitude of the noise. The superposition of air under pressure in the expansion tube suppresses the excitations in the fluid which accompany the escape of gases as the fluid is heated. Driving ofl these gases would normally result in turbulence and noise. The superposition of the air pressure in the expansion tube damps out much of this turbulence, and relieves the excitation which would otherwise set the metallic heater unit into noisy vibrations. Thus the sizzling noises encountered on start up and, which occur before the boiling point of the fluid is reached, are suppressed and the time interval that they are manifest is decreased by the superatmospheric air provided in the expansion tube. Noise which might otherwise result from localized vaporization of water in direct contact with the heating element, is apparently similarly suppressed.

The general purpose of this invention is to provide both method and apparatus for an electrical baseboard heater which possesses none of the aforedescribed disadvantages. An object of the present invention is to provide an electrical baseboard heater which incorporates, within the self-contained unit, means for suppressing the noises customarily generated in the operation of such heater. To this end, a specific purpose is the provision of a method of producing electrical baseboard heaters wherein the noises accompanying start up are suppressed.

In the present invention these objects and purposes (as well as others apparent herein) are achieved generally by providing an electrical baseboard heater having a closed tube passage for circulation of a heat transfer liquid including a liquid reservoir portion in which is housed an electrical heating element. A tube is provided with its lower end opening into the continuous liquid passageway; and above the level of the passageway the tube serves as an expansion chamber. The expansion tube is sealedly closed at its upper end and filled with a gas substantially in excess of atmospheric pressure.

Such an electrical baseboard heater is charged, in the present invention, by the method of filling, through the originally open upper end of the expansion tube, the circulation passage with a heat transfer liquid at atmospheric pressure; and then filling the expansion tube itself with a gas at a pressure substantially above atmospheric pressure. The upper end of its expansion tube is then sealed, thereby to provide a self contained heater unit having a compressed gas therein.

Utilization of the invention will become apparent to those skilled in the art from the disclosure made in the following description of a preferred embodiment of the invention as illustrated in the accompanying drawing, in which:

FIG. 1 is a side elevational view of the electrical base board heater of the present invention, and broken away in parts to show the internal components; shown with the charging air supply attached;

FIG. 2 is an end view of the preferred embodiment shown in FIG. 1;

FIG. 3 is a sequential representation of the charging and closing operation performed at the upper end of the expansion chamber during fabrication of the heater; and

FIG. 4 is a graphical representation indicating generally the noise levels during start up as a function of time for various selected pressures provided within the expansion chamber of the heater before sealing it.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a baseboard heating element assembly, generally designated 10, which is comprised of a continuous and sealed tubular circulation passage generally designated 12, and an expansion tube 14. On the circulation passage are mounted fins 34, hereinafter described, which for clearer illustration are shown in FIG. 1 rotated The tubular circulation passage 12 is preferably copper tubing and consists of a lower passage tube 16 and an upper passage tube 18, the lower passage tube 16 having a liquid reservoir portion 20, which is of somewhat greater diameter. The lower passage tube 16 extends horizontally from a necked-down junction at the other end of the reservoir portion 20 and bends upwardly at its far end there to communicate with the horizontally extending upper passage tube 18. The upper tube 18 has a downward bend which communicates with the upper wall of the reservoir portion 20 near one end thereof. The circulation tube, just described, provides a flow path for heated liquid from the reservoir por tion 20, through the upper fin tube 18 and then back to the reservoir portion 20 by means of the lower passage tube 16. The volume of this circulation path may vary upon the particular application of the baseboard heating assembly 10. In a particular model heater made up as shown in the illustrated embodiment, this volume is approximately l50 cubic inches.

The liquid reservoir portion 20 is provided with an electrical heating element 22 mounted spacedly therein. The inner conductor and insulation portion of the heating element are shown broken to reveal the full interior of the liquid filled reservoir portion 20. At the end opposite the necked-down junction, the reservoir 20 is closed by sealing cap 24 having electrical insulative bushings which mount and support the heating element 22. The electrical heating element 22 is preferably a hairpin-shaped resistive wire, such as Nichrome wire, which is enclosed in suitable insulating material wrapped in a copper sheath. External electrical contact with the resistive wire is made by means of two threaded 'studs 26 extending through the sealing cap 24. These threaded studs 26 are provided with threaded nuts 28 which secure electrical lead wires which connect the heating element to a conventional source of electrical energy, as shown. To the reservoir portion 20 there is attached a mounting bracket 30. The bracket 30 is provided with holes 32 through which bolts are inserted to secure the baseboard heating assembly 10 to a decorative and air-conducting cabinet (not shown). In the embodiment shown, the electrical heating element 22 is preferably rated at 2,000 watts.

Secured onto the upper passage tube 18 is an aluminum, accordion-like box fin construction 34 which increases the surface area of the heat exchange system and permits effective radiation of heat from the upper passage 18 to the air circulating through the cabinet. The fin construction is shown at each end and removed in the intermediate portion to reveal the upper tube 18. A heat exchange liquid, designated 36, fills the circulation passage to the level indicated by the fill-level line I. Preferably the heat exchange liquid is a mixture of anti-freeze solution and water; for example, one part of ethylene glycol mixed with three parts of water by volume. The anti-freeze solution tends to raise the boiling point of the system so that the baseboard heater assembly will operate at a sufficiently high temperature without approaching the boiling point of the liquid.

The expansion tube 14 branches upwardly from the intersection of the upper and lower passage tubes 16 and 18 to form an expansion chamber designated 38. This expansion tube 14 is sealed at its upper end 40 and provides for the expansion of the heat transfer liquid 36. In the illustrated embodiment the expansion chamber 38 has a volume of approximately 19 cubic inches. The size of this expansion chamber 38 is chosen in relation to the capacity of the circulation tube 12 and expansion ratio of the particular liquid used to fill it. The chamber 38 may vary in maximum size, but it must be of at least sufficient volume to permit the anticipated expansion of the liquid at the operating level .of the heater 10 and then provide substantial excess volume to be occupied by a compressed gas; hence in heating the gas, pressure will not be so greatly increased as to damage the heater.

There is provided in the expansion chamber 38 a gas as indicated at 42. This gas has a pressure substantially greater than atmospheric pressure'when the heat exchange liquid 36 is unheated, which pressure is supplied by the method of charging the heater as described hereinafter.

It is essential, in practicing the present invention, that prior to such heating, the gas presure within the expansion chamber 38 should be preferably approximately pounds per square inch and, in any event, within the range from 10 pounds per square inch to pounds per square inch above atmospheric pressure. Although air has been set 'forth as the gas which occupies the expansion chamber 38, any suitable gas capable of being compressed to a pressure within the indicated range above atmospheric pressure could be used.

One method of charging the electrical baseboard heating assembly 10 so that start up noises are suppressed is as follows: During the forming of the baseboard heater 'assembly 10 and before the upper end 40 of the expansion tube 14 is closed, a solution of water and anti-freeze in the ratio of approximately three parts to one part, respectively, by volume is prepared. This solution is thoroughly mixed and then introduced into the baseboard heating assembly 10 by pouring it into the opening 44 (see FIG. 3A) in the upper end 40 of the expansion chamber 14. Sufficient anti-freeze and water solution 36 is introduced into the heater to fill it to the fill line I. After the solution has been introduced, it is agitated slightly to insure that air pockets are discharged from the circulation tube 12. Next, at atmospheric pressure, a process tube 48 having a hollow passage 49 therethrough is inserted partially into the chamber 38 as shown in FIG. 3A. To insure an air-tight seal, the upper end 40 is then crimped around the tube 48 and a brazed joint provided between them to result in the construction shown in FIG. 3B.

The protruding end of the process tube 48 is connected to an air pressure supply, shown diagrammatically at 50 in FIG. 313. Air under pressure is then supplied to the expansion chamber through the process tube 48. When the air pressure within the tube has reached the predetermined value, which in the specific embodiment described is chosen at approximately 30 pounds per square inch, a conventional relief valve (not shown) will open to indicate that the desired pressurization of the expansion chamber has been accomplished.

The expansion chamber is sealed by crimping the protruding end of the small process tube 48, after which the air supply 50 is removed and the protruding crimped end 52 trimmed and permanently sealed by brazing it to the expansion chamber 14.

In operation, the baseboard heating assembly 10 is energized by attaching electrical conductive wires, as shown, to the threaded studs 26. The conductive wires are then connected to a source of electrical energy 54. Current flows from the source of electrical energy 54, through the conductive studs 26, through the hair-pin Nichrome wire heating element 22, and back to the source 54. As the electrical heating element 22 becomes ener gized, the surrounding heat transfer liquid 36 in the reservoir portion 20 begins to heat. This heating tends to drive off the entrained air present in the liquid, thereby generating the start up noises and turbulence referred to hereinabove. The escape of this entrained air and accompanying turbulence and noise are somewhat suppressed by the pressurized gas in the expansion chamber 38.

As the heat transfer liquid in the reservoir continues to be heated, a temperature gradient results in the flow of heat transfer liquid 36 from the reservoir portion 20,

ly 25 minutes to approximately 8 minutes.

. teachings.

expands into the expansion chamber 14 and further compresses the initially compressed gas provided therein.

FIG. 4 shows the effect of pressurizing the expansion chamber before it is sealed. As indicated by the family of curves, the time after start up during which noise materially manifests itself is decreased significantly; and besides there appears to be a noticeable diminution of the maximum noise level. This graphical representation of FIG. 3 is based on sensory comparisons.

The initial pressurization has a remarkable effect in decreasing the time of noisy operation, as is manifest from the decreasing time intervals shown by the curves of FIG. 3 for zero initial pressure and each successive l0 p.s.i. increment. For example, comparing the relatively low pressurization of 20 p.s.i. with no initial pressurization, the noisy time is decreased from approximate- A further pressurization increase to the preferred 30' p.s.i. reduces the noisy period to about 5 minutes. The upper limit of the range of pressures which is feasible in any heater isdetermined by its structural parameters, i.e. the tubing strength, liquid volume vs. expansion volume, etc. At present, initial pressurization of approximately 40 p.s.i. is considered the approximate effective safe upper limit.

Thus, it may be seen from the foregoing disclosure that the pressure-charging of the expansion chamber of the baseboard heating assembly has an important effect on the commercial acceptability of such heaters, in that it greatly reduces the offensiveness of noises accompanying .start up and thermostatic cycling of such heaters.

Obviously many modifications and variations of the present invention are possible in the light of the above It is therefore to be understood that, within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. The method of charging an electrical baseboard heater of the type having a continuous and sealed liquid circulation passage, an electrical heating element sealed therein, and an expansion chamber communicating with the passage and extending upwardly therefrom to an upper chamber end opening, comprising the steps of filling a heat transfer liquid at room temperature and atmospheric pressure through the upper end opening of the expansion chamber in a quantity sufiicient to fill the liquid circulation passage,

pressure-filling the expansion chamber with a gas through said upper end opening to a pressure substantially above atmospheric pressure, and

then permanently sealing said upper end opening of the expansion chamber,

whereby the excess pressure over atmospheric pressure suppresses noises attendant to heating the heat transfer liquid.

2. The method of charging .an electrical baseboard heater as defined in claim 1, wherein the gas is air under a pressure of substantially 30 pounds per square inch above atmospheric pressure, whereby on heating the rate of escape of entrained gases from the liquid is lessened and excitations accompanying such escape are suppressed.

3. The method of charging an electrical baseboard heater as defined in claim 1, wherein the gas is air under a pressure within the range from pounds per square inch to 40 pounds per square inch above atmospheric pressure.

4. An electrical baseboard heater, comprising a continuous and sealed tubular liquid circulation passage having a liquid reservoir portion therein,

an electric heating element sealed within said liquid reservoir portion,

an expansion tube branching at its one end from said liquid circulation passage and extending upwardly therefrom forming an expansion chamber therewithin, said expansion tube being sealed at its other end, and

a heat exchange liquid within said liquid circulation passage and said reservoir and extending into said first end of said expansion tube,

said expansion tube having a gas therein, the pressure of said gas when the heat exchange liquid is unheated being substantially greater than atmospheric pressure,

whereby the excess pressure over atmospheric pressure suppresses noises attendant to heating the heat transfer liquid.

5. An electrical baseboard heater of claim 4 wherein said gas is air under a pressure of between 10 pounds and pounds per square inch above atmospheric pressure.

References Cited by the Examiner UNITED STATES PATENTS 1,655,277 1/1928 Madsen 237-8 X 1,919,204 7/1933 Decker 219341 2,522,373 9/1950 Jodell 12232 2,772,342 11/1956 Reynolds et a1. 219-341 3,179,788 4/1965 Uhlig 219341 RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner.

C. L. ALBRI'ITON, Assistant Examiner. 

1. THE METHOD OF CHARGING AN ELECTRICAL BASEBOARD HEATER OF THE TYPE HAVING A CONTINUOUS AND SEALED LIQUID CIRCULATION PASSAGE, AN ELECTRICAL HEATING ELEMENT SEALED THEREIN, AND AN EXPANSION CHAMBER COMMUNICATING WITH THE PASSAGE AND EXTENDING UPWARDLY THEREFROM TO AN UPPER CHAMBER END OPENING, COMPRISING THE STEPS OF FILLING A HEAT TRANSFER LIQUID AT ROOM TEMPERATURE AND ATMOSPHERIC PRESSURE THROUGH THE UPPER END OPENING OF THE EXPANSION CHAMBER IN A QUANTITY SUFFICIENT TO FILL THE LIQUID CIRCULATION PASSAGE, PRESSURE-FILLING THE EXPANSION CHAMBER WITH A GAS THROUGH SAID UPPER END OPENING TO A PRESSURE SUBSTANTIALLY ABOVE ATMOSPHERIC PRESSURE, AND THEN PERMANENTLY SEALING SAID UPPER END OPENING OF THE EXPANSION CHAMBER, WHEREBY THE EXCESS PRESSURE OVER ATMOSPHERIC PRESSURE SUPPRESSES NOISES ATTENDANT TO HEATING THE HEAT TRANSFER LIQUID. 